The invention relates generally to a rotary machine, and in particular to an apparatus and method for controlling rotational speed of a component of the rotary machine by using pressurized gas.
Rotary machines include, without limitation, turbines for steam turbines, compressors and turbines for gas turbines and turbines for hybrid fuel cells. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a steam generating device, a turbine and a steam outlet. A gas turbine has a gas path that typically includes, in serial-flow relationship, an air intake (also known as an inlet), a compressor, a combustor, a turbine, and a gas outlet. A hybrid fuel cell has a gas path that typically includes, in serial-flow relationship, an air intake, a compressor, a fuel cell, a turbine and a gas outlet. In the abovementioned turbines, the gases (steam or gas) flow to a turbine that extracts energy for driving a turbine shaft to produce output power for powering an electrical generator. A turbine is typically operated for extended periods of time at a relatively high base load for powering the electrical generator to produce electrical power in a utility grid, for example. In some cases, the rotary machine is subject to a grid transient or load interruption that causes the output breakers of the electrical generator to open thereby resulting in a sudden loss of load that can cause an overspeed condition. The loss of load, in addition to a response time of the rotary machine to the load interruption, may cause an acceleration effect to the rotary components and, at times, result in mechanical damage therein.
In the case of a free-spinning turbomachinery component, such as an unloaded turbine, rotational speed control requires application of torque to the shaft of the turbomachinery component. Previous methods of rotational speed control include the use of a relatively complex mechanical and/or electrical system to provide a load to the shaft. Although such systems are acceptable for most applications, there is a need to provide a simple, reliable, repeatable, lightweight, and inexpensive apparatus and method to impart a torque to a rotating shaft of turbomachinery component without the use of a relatively complex mechanical and/or electrical system.